Amplitude and phase light modulator based on miniature optical resonators
The systems described herein can be used to modulate either the phase, the amplitude, or both of an input light wave using micro-resonators to achieve desired degrees and/or types of modulation.
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This application claims the benefit of U.S. Provisional Patent Application No. 62/838,084, filed on Apr. 24, 2019, and U.S. Provisional Patent Application No. 62/828,261, filed on Apr. 2, 2019, the entirety of which are both incorporated by reference herein.
GRANT INFORMATIONThis invention was made with government support under grant numbers HR00111720034 awarded by the Defense Advanced Research Project Agency (DARPA) and FA9550-14-1-0389 awarded by the Air Force Office of Scientific Research (AFOSR MURI). The government has certain rights in the invention.
BACKGROUNDCertain optical modulators can be used in photonic systems for on-chip optical routing and free-space wavefront shaping. For example, certain optical amplitude modulators and optical phase modulators can be employed to realize a diverse range of applications, including optical switching fabrics, artificial neural networks, light ranging and detection, free-space optical communication, phased-array imaging, augmented and virtual reality display, quantum information processing, nonlinear optics, optical sensing, and optogenetics.
Certain optical phase modulators can be based on phase accumulation through light propagation in a waveguide with tunable refractive indices. Due to the narrow refractive index change of certain materials induced by thermo-optic or electro-optic effect, a phase shifter can demand a long propagation length (e.g., in the range of 1-10 mm) leading to increased system size. Although certain plasmonic structures can enhance light-matter interaction and reduce system size, they can amplify device insertion losses. Certain resonant structures can be employed to improve performance of amplitude modulators. However, such resonant structures can provide a narrow range of phase modulation.
Thus, there is a need for improved techniques for controlling a spatial distribution of amplitude and phase of light to improve the performance of a photonic system or to realize new system functionalities.
SUMMARYThe disclosed subject matter provides systems and methods for controlling the amplitude and phase of light in connection with a photonic system.
In certain embodiments, a photonic system is disclosed which can control spatial distribution of amplitude and phase of light using an array of pixels. In non-limiting embodiments, the disclosed system can include at least one 1D or 2D array of pixels. Each pixel can include a device to modulate amplitude and/or phase of light waves propagating in a waveguide. The device can be a phase modulator and/or an amplitude modulator. In some embodiments, the device can include an optical micro-resonator. The disclosed photonic system can control and/or adjust interactions between guided light waves and the optical micro-resonator through a signal tuner that reacts to external electric signals and can alter the reflective index of the optical micro-resonator. For example, a voltage can be applied to a micro-heater or a pair of electrodes to tune the resonance frequency of the optical resonator resulting in amplitude and phase change.
In certain embodiments, the system can include a platform of integrated photonics. For example, the platform can include an integrated Si, an integrated LiNbO3, an integrated Si3N4, and/or transition metal dichalcogenide (TMD) monolayers. The platform can operate in the visible (e.g., λ=400˜700 nm) and telecommunications (e.g., λ=˜1.55 μm) bands. In non-limiting embodiments, the platform can further include at least one micro-heater. In some embodiments, the disclosed system with the integrated LiNbO3 platform can include at least two electrodes patterned on the two sides of the resonator. A control voltage can be applied between the electrodes and produce an in-plane electric field in the transverse direction with respect to the light propagation direction in the system. This electric field can induce a change in the refractive index of LiNbO3 through the electro-optical effect, which can lead to modulation of light transmitted through the device. The integrated LiNbO3 platform can provide an increased modulation speed (e.g., >1 GHz).
In certain embodiments, the optical resonator can be a ring resonator and/or a disk resonator. The optical resonator can be coupled to waveguides through evanescent coupling. In non-limiting embodiments, the optical resonator can be a one-dimension (1D) photonic crystal cavity embedded in waveguides. The disclosed 1D photonic crystal resonators can provide a reduced footprint, e.g., 2 micron×20 micron in the NIR and 1 micron×10 micron in the VIS. In non-limiting embodiments, structural parameters of the resonators can be adjusted to provide target resonance frequencies and coupling strengths of resonant modes. The frequency of resonant mode can further be tuned by adjusting the material refractive index of the optical resonator, e.g., by applying a voltage. In-some embodiments, a target frequency can be achieved through thermo-optic effects via a micro-heater. In certain embodiments, the target frequency can be achieved through electro-optic effects via electrodes. In non-limiting embodiments, the target frequency can be achieved through field effects that can change carrier concentrations on TMD monolayers of the system.
Interference between a background signal and the resonator output can help achieve pure phase modulation, i.e., a 2π phase modulation with minimal amplitude modulation. For example, in a 1D photonic crystal resonator, the background signal can be produced by reflection, such as by inclusion of two back-to-back width perturbed distributed Bragg reflectors or DBRs, which can generate a reflection. In a micro-ring resonator, the background can be provided by direct transmission through the waveguide. In certain embodiments, the disclosed system can provide a near 2π pure phase modulation. For example, the disclosed system can provide the near 2π pure phase modulation by coupling of light from waveguide into a resonator one order of magnitude larger than the decay rate due to the combination of scattering, bending, and absorption losses in the resonator (i.e., over-coupling regime). In non-limiting embodiments, the disclosed system can include at least two resonators. For example, two ring resonators with the same resonant frequency can be cascaded to provide 4π phase modulation across the resonance.
In non-limiting embodiments, the disclosed system can provide a 0-100% amplitude modulation. For example, the disclosed system can provide the 0-100% amplitude modulation by coupling light from waveguides to resonators, where the coupling rate is equal to the sum of scattering and absorption losses in the resonator (which can be referred to as a critical-coupling regime). In non-limiting embodiments, micro-resonators can be designed to operate in such a critical coupling regime where across a resonance the optical amplitude can have a complete variation from 0 to 1.
In some embodiments, the disclosed system can provide a near 2π pure phase modulation and a 0-100% amplitude modulation by combining the amplitude modulator and the pure phase modulator. The combination of the amplitude modulator and the pure phase modulator can provide independent and complete modulation of amplitude and phase of light in a waveguide. For example, a first micro-resonator operating in the critical coupling regime and a second micro-resonator operating in the strongly over-coupling regime can provide complete and independent modulation of optical amplitude and phase.
In certain embodiments, the disclosed system can convert amplitude and phase distributions of light on the pixel array to amplitude and phase distributions of light in the far-field, and vice versa. For example, the disclosed system can be employed in a projector configuration and convert light propagating in waveguides into far-field radiation. The wavefront of the far-field radiation can be controlled by electrical signals applied to the pixel array. In non-limiting embodiments, the disclosed system can be employed in a holography projector and provide a complete and dynamic control of amplitude and phase distributions of light in the far-field (i.e., dynamic 3D display). In some embodiments, the disclosed system can provide independent control of light. For example, the system can function as a pure amplitude spatial light modulator or a phase spatial light modulator. The pure phase spatial light modulator can steer a coherent light beam over a solid angle in the far-field.
In certain embodiments, the disclosed system can provide pure-phase modulation with zero insertion losses. For example, an input mode can couple into a pair of identical 1D photonic crystal resonators through a multimode interference (MMI) device. The two 1D resonators can share the same control voltage or control micro-heater so that they can be modulated by the same degree. The 1D resonators can be terminated with distributed Bragg reflector (DBR) gratings and produce two modulated reflected light waves that constructively interfere to couple all optical power into an output port. The output signal can have a 2π modulation and minimal amplitude variation across an optical resonance.
In certain embodiments, the disclosed system can be employed in a detector configuration and convert an incident light beam from the far field into a waveguide output. For example, a light beam incident from a specific angle can couple into the pixel array, then into the waveguide array associated with the pixel array, and then into a guided wave in the bus waveguide, which can be detected. In non-limiting embodiments, a light detection and ranging (LIDAR) system can combine the projector and detector functions in a single system. For example, the LIDAR system can be created based on optical micro-resonators. A phased array of micro-ring resonators can operate in the over-coupling regime and control a beam steering in a first direction. Beam steering in a second direction can be controlled by an array of 1D photonic crystal modulators that can be side-coupled to waveguides. A 1D modulator can be tuned to be on resonance with the wavelength of the incoming light and resonantly scatter the light vertically out with decreased in-line transmission and reflection. In some embodiments, the modulator can be off resonance with the incoming light, and the light can pass through the waveguide with high transmission. In non-limiting embodiments, the LIDAR system can be used in the transmitter mode and/or receiver mode.
For example, a cylindrical lens can be placed above the array of 1D photonic crystal modulators, which can translate the emission from different columns of the 1D modulators to different emission angles in the far field. The lens can provide for independent control of the beam. In a receiver mode, the angular positions along the first and second directions of the incoming beam can be determined by certain column of 1D photonic crystal resonators that can tuned to be on resonance with the frequency of the incoming light, and the phase gradient used by the array of micro-ring resonators.
In certain embodiments, the disclosed system can provide a decreased device footprint, a reduced power consumption, and an improved operating speed for photonic systems. The disclosed system can modulate spatial light for both amplitude and phase simultaneously (or independently) based on optical resonators.
In certain embodiments, the disclosed system can be employed in an augmented reality (AR) or a virtual reality (VR) system. For example, the disclosed system can provide a holographic display screen in the AR/VR system. In non-limiting embodiments, the disclosed system can be employed in an optical network-on-chip (ONoC) for optical communication and processing.
Reference will now be made in detail to the various exemplary embodiments of the disclosed subject matter which are illustrated in the accompanying drawings. The systems and methods described herein can be used, for the purpose of example and not limitation, to control the spatial distribution of amplitude and phase of light using a plurality of pixels. The disclosed systems and methods can control and/or adjust interactions between guided light waves and an optical micro-resonator through a signal tuner that reacts to external electric signals.
In an exemplary general case, illustrated in
Wherein ω0 is the resonant frequency, 1/τ0 is the decay rate due to loss, 1/τe is the decay rate due to outgoing radiation, including coupling into a j-th radiation channel 103 which leaves the resonator, and κe characterizes a coupling between the excitation field and a resonant mode. Assuming that the harmonic excitation has a time dependence of ejωt, Eq. 1 yields:
Thus, the electric field in the j-th radiation channel 103 is given by the equation:
Eout=κja (3)
The amplitude response 111 and the phase response 112 are shown by
with a center at
It follows that if one can bring the center of the trajectory circle to the origin, there will be a pure phase modulation without amplitude modulation. The present disclosure achieves this result by adding to the resonator radiating field 103 a background field 105 which modifies Eq. 3 to become:
The result of adding the background field 105 to the resonator 101 is shown in
In one exemplary embodiment, pure-phase modulation can be achieved by the use of micro-resonators in a strongly over-coupled regime. A strongly over-coupled regime refers to a situation where the coupling rate between a resonator and a waveguide is much larger than the decay rate due to the combination of scattering an absorption loses in the resonator. The Q factor can be related to the decay rate by Q=ωτ/2, and therefor QLoad<<Q0/2, where QLoad and Q0 are, respectively the loaded/external and intrinsic Q factors of the resonator.
Another exemplary embodiment is shown by
The term “about” or “approximately” means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e., the limitations of the measurement system. For example, “about” can mean within three or more than three standard deviations, per the practice in the art. Alternatively, “about” can mean a range of up to 20%, up to 10%, up to 5%, and up to 1% of a given value.
In another exemplary embodiment, as illustrated by
While in the exemplary embodiment illustrated in
In an exemplary adiabatic ring, for example,
Another exemplary embodiment of the disclosed subject matter, namely pure phase modulation based on micro-disk resonators operating in the visible spectral range, is illustrated in
Similar results can be observed at different wavelengths. For the purpose of example and not limitation, where the wavelength is 530.48 nm, as in
For the purpose of comparison and example rather than limitation, optical modulators can be fabricated based on MZI structures which consist of bare waveguides with varied arm lengths, for example between 300 and 500 micrometers, as illustrated in
where neff is the effective group modal index of the resonant mode and Lcav is the resonator cavity length. Additionally combining Eq. 6 with
where t is the minimum amplitude at the center of the resonance, suggests that in order to reduce power consumption of the phase modulator, Qload should be as large as possible and the footprint of the cavity (Lcav) as small as possible. Additionally, the ratio of Qload to Q0 should be kept as small as possible in order to prevent significant amplitude variation. Another advantage of the presently disclosed subject matter is that the disclosed embodiments have a linear dimension of about 1/10 that of the MZI devices of
Pure phase modulation in an adiabatic micro-ring resonator 601 is demonstrated in
Various exemplary embodiments have been created and tested.
In addition to the embodiments already disclosed, the presently disclosed subject matter also contemplates using multiple subordinate micro-resonators in series or arranged in an array. For the purposes of example and not limitation,
In addition to pure phase modulation, the presently disclosed subject matter also contemplates pure amplitude modulation. Micro-resonators are contemplated which, when operated in a critical coupling regime, result in an optical variance from 0 to 1 across the resonance. One potential application of the presently disclosed subject matter is a first micro resonator operating in the critically coupled regime and a second micro resonator operating in the strongly over-coupled regime, which can then provide complete and independent modulation of optical amplitude and optical phase.
The predicted results of the embodiment of
In recent years, lithium niobate has become a viable platform for integrated photonics. Single-crystal lithium niobate thin films with, for example, 300 nm and 1 μm in thickness, about 3 inches in size, and with a low density of impurities and vacancies are now commercially available. Further, MgO-doping and “optical cleaning” have drastically improved the optical damage threshold of lithium niobate, enabling an integrate lithium niobate platform to carry high optical power up to 1000 W/cm2. Novel cleanroom recipes can be used to nanostructure lithium niobite, resulting in the devices illustrated in
The presently disclosed subject matter contemplates integration of the 1D modulator design of
A further embodiment of the presently disclosed subject matter contemplates a 1D modulator design based on integrated silicon nitride (Si3N4) and transition metal dichalcogenide (TMD) monolayers. Such a design is illustrated, for the purpose of example and not limitation, in
In certain disclosed embodiments, the 1D photonic crystal resonator modulates the in-line transmission through the exemplary devices. The presently disclosed subject matter also contemplates directing the modulated light into free space without additional out-couplers, such a device is illustrated in
Pure phase modulation with zero insertion losses can be realized in 1D modulators using a device configuration illustrated in
The presently disclosed subject matter also contemplates a light detection and ranging (LIDAR) system composed of optical micro-resonators.
Furthermore, the system 2900 can be used in a receiver mode. The angular positions along the x and y directions of the incoming beam that can be detected are determined, respectively, by the specific column of the 1D photonic crystal resonators that is tuned to be on resonance with the frequency of the incoming light, and the phase gradient used by the array of micro-ring resonators. It is further contemplated that the system 2900 can be used as a light projector or a spatial light modulator, which generates a desired output beam but does not collect incoming light.
In addition to the various embodiments depicted and claimed, the disclosed subject matter is also directed to other embodiments having other combinations of the features disclosed and claimed herein. As such, the particular features presented herein can be combined with each other in other manners within the scope of the disclosed subject matter such that the disclosed subject matter includes any suitable combination of the features disclosed herein.
The foregoing description of specific embodiments of the disclosed subject matter has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosed subject matter to those embodiments disclosed.
It will be apparent to those skilled in the art that various modifications and variations can be made in the methods and systems of the disclosed subject matter without departing from the spirit or scope of the disclosed subject matter. Thus, it is intended that the disclosed subject matter include modifications and variations that are within the scope of the appended claims and their equivalents.
Claims
1. A system for producing pure phase modulation of an input light wave comprising:
- a curved waveguide for receiving the input light wave;
- a micro-resonator coupled to at least a portion of the curved waveguide, wherein a gap of at least about 150 nm exists between the micro-resonator and the curved waveguide and the micro-resonator has a length or a radius of at least 15 μm and is configured to produce pure phase modulation of the input light wave by operating in a strongly over-coupled regime;
- a signal tuner proximate to the micro-resonator, wherein the signal tuner is adapted to alter a refractive index of the micro-resonator; and
- an output, coupled to the micro-resonator to output the purely phase modulated light.
2. The system of claim 1, wherein the signal tuner is a micro-heater adapted to alter the refractive index of the micro-resonator through a thermo-optical effect.
3. The system of claim 1, wherein the signal tuner is a pair of micro-electrodes adapted to alter the refractive index of the micro-resonator through an electro-optical effect.
4. The system of claim 1, wherein the micro-resonator is a 1D photonic crystal, wherein the input light wave is reflected by a cavity of the 1D photonic crystal to produce pure phase modulation.
5. The system of claim 1, wherein the micro-resonator is a micro-ring evanescently coupled to the curved waveguide and configured to operate in a strongly over-coupled regime.
6. The system of claim 5, wherein the micro-ring is an adiabatic ring, wherein
- a narrow portion of the ring is located adjacent to the portion of the curved waveguide to which the resonator is coupled for strong coupling between the micro-ring and the waveguide;
- a wide portion of the ring is located some distance from the waveguide and is configured to reduce scattering losses from roughness of a sidewall of the micro-ring.
7. The system of claim 1, wherein the micro-resonator is a micro-disk.
8. The system of claim 1, wherein the waveguide is coupled to the micro-resonator by wrapping a portion of the waveguide around the micro-resonator.
9. The system of claim 1, wherein the micro-resonator comprises a plurality of subordinate micro-resonators arranged in arrays.
10. The system of claim 1, wherein the micro-resonator is composed of material selected from the group consisting of silicon, germanium, silicon nitride, aluminum nitride, silicon dioxide, lithium niobate, diamond, and compound semiconductors.
11. The system of claim 1, wherein the curved waveguide is a pulley waveguide, extending around a majority of the circumference of the micro-resonator.
12. A system for producing phase and amplitude modulation of an input light wave comprising:
- a fixed-curved waveguide for receiving the input light wave;
- a first micro-resonator coupled to at least a first portion of the curved waveguide, wherein a gap of at least about 150 nm exists between the micro-resonator and the curved waveguide and the micro-resonator has a length or a radius of at least 15 μm and is and configured to produce pure phase modulation of the input light wave by operating in a strongly over-coupled regime;
- a second micro-resonator coupled to at least a second portion of the curved waveguide and configured to produce pure amplitude modulation of the input light wave by operating in a critically coupled regime;
- a plurality of signal tuners proximate to each of the first and the second the micro-resonators, wherein the plurality of signal tuners are adapted to alter a refractive index of the first and the second micro-resonators; and
- an output, coupled to the micro-resonators to output the phase and amplitude modulated light.
13. The system of claim 12, wherein the signal tuner is a micro-heater adapted to alter the refractive index of the micro-resonator through a thermo-optical effect.
14. The system of claim 12, wherein the signal tuner is a pair of micro-electrodes adapted to alter the refractive index of the micro-resonators through an electro-optical effect.
15. The system of claim 12, wherein the micro-resonator is a 1D photonic crystal.
16. The system of claim 15, wherein the 1D photonic crystal is further configured to direct the modulated light wave into free space, wherein the 1D photonic crystal comprises a perturbation in the 1D photonic crystal.
17. The system of claim 16, wherein the perturbation in the 1D photonic crystal comprises a second order grating which scatters the modulated light wave in a direction perpendicular to an in-line transmission direction of the input light wave.
18. The system of claim 12, wherein the micro-resonator comprises a plurality of subordinate micro-resonators arranged in arrays.
19. The system of claim 12, wherein the micro-resonators are composed of materials selected from the group consisting of silicon, germanium, silicon nitride, aluminum nitride, silicon dioxide, lithium niobate, diamond, and compound semiconductors.
20. The system of claim 12, wherein the curved waveguide is a pulley waveguide extending around a majority of the circumference of the first micro-resonator.
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Type: Grant
Filed: Apr 2, 2020
Date of Patent: Aug 22, 2023
Patent Publication Number: 20220308370
Assignee: The Trustees of Columbia University in the City of New York (New York, NY)
Inventors: Guozhen Liang (Singapore), Heqing Huang (Bronx, NY), Michal Lipson (New York, NY), Nanfang Yu (Fort Lee, NJ)
Primary Examiner: Rhonda S Peace
Application Number: 16/838,714
International Classification: G02B 6/12 (20060101); G02B 6/293 (20060101); B82Y 20/00 (20110101); G02F 1/035 (20060101); G02B 6/122 (20060101); G02F 1/01 (20060101); G02F 1/21 (20060101); G02F 1/225 (20060101);